Community Antenna Television ("CATV") systems are used in a widespread manner for the transmission and distribution of television signals to end users, or subscribers. In general, CATV systems comprise a transmission subsystem and a distribution subsystem. The transmission subsystem obtains television signals associated with a plurality of CATV channels and generates a broadband CATV signal therefrom. The distribution subsystem then delivers the CATV broadband signal to television receivers located within the residences and business establishments of subscribers. The complexity and size of the distribution subsystem requires that operation and performance be periodically tested and/or monitored.
Two tests often performed by CATV service providers are signal level monitoring and leakage detection. CATV service providers use signal level monitors to measure the signal level of particular channel frequencies at any part of the distribution subsystem. A technician connects the signal level monitor to the coaxial cable at any location within the distribution subsystem. The signal level monitor allows the technician to obtain data regarding the frequency response of the distribution subsystem and identify distribution subsystem and transmission subsystem related problems.
Leakage detectors are devices that detect and/or measure the leakage of a broadband CATV signal from the distribution subsystem. Leakage refers to the transmission of signals through breaches or other nonconformities in the CATV distribution subsystem. In particular, the distribution subsystem, which typically comprises coaxial cable, amplifiers and other devices, ideally provides a relatively low-loss conduit between the CATV transmission subsystem and subscribers' television receivers. If, however, portions of the distribution subsystem are physically damaged, for example, the coaxial cable is damaged, kinked or broken, then the broadband CATV signal or portions thereof may leak through the damaged distribution subsystem causing unwanted transmission into the atmosphere. Since portions of the allocated CATV bandwidth overlap with frequencies allocated for aeronautical communication, excessive leakage of CATV signals can therefore undesirably interfere with aeronautical-related signal transmission and reception. As a result, government regulations permit only a finite level of CATV signal leakage. Leakage detectors help determine compliance with government regulations and can otherwise provide information as to the performance of particular sections of the distribution subsystem.
Signal level monitoring and leakage detection techniques typically use the signal level of the horizontal or vertical synchronization pulse of a television signal to provide an accurate and consistent measurement. To this end, signal level monitoring and leakage detection devices typically demodulated a television signal to be tested to obtain a baseband signal. Such devices then used analog or digital techniques to measure the level of either the vertical or horizontal synchronization pulses in the baseband signal.
A drawback to prior art signal level monitoring devices and leakage detection devices is their component cost. The circuitry used in such devices, including the analog circuitry used to perform demodulation of the television signal to be tested, adds significantly to the product cost. Furthermore, prior art signal level monitoring devices and leakage detection devices that utilize analog measurement circuitry suffer from additional drawbacks that are overcome by digital measurement circuitry. For example, due to component variances, analog measurement circuitry, requires calibration in order to obtain accurate readings; however, digital measurement circuitry does not effectively exhibit such variances. Furthermore, unlike digital measurement circuitry measurement levels provided by analog measurement circuitry will be effected due to age and temperature of the analog components comprising the analog measurement circuitry. Analog measurement circuitry is also not easily altered in order to perform additional functions or improvements over existing functions. Digital measurement circuitry, however, may be altered by simply providing the digital measurement circuitry with new software routines software upgrades.
Accordingly, there is a need for a signal level monitoring device that reduces component requirements in order to reduce its cost and that provides for digital measurement of the monitored signal level in order to overcome the above drawbacks of analog measurement. Likewise, there is a need for a leakage detection device that reduces component requirements in order to reduce its cost and that provides for digital measurement of the leakage signal level in order to overcome the above drawbacks of analog measurement.